revert: remove hf_oauth and LoginButton (OAuth was a misdiagnosis)

The original 'GPU quota exceeded' issue turned out to be a contextvar
propagation bug in our worker thread, not a Pro-attribution issue.
ZeroGPU reads identity from the X-IP-Token header that HF's reverse
proxy sets from the standard huggingface.co cookie — completely
independent of OAuth. Once 1e054fe propagated the Gradio request
contextvar to the worker thread, attribution worked without OAuth.

Removing the unused machinery:
- README hf_oauth: true -> false
- README hf_oauth_expiration_minutes (delete)
- app.py: drop the gr.LoginButton + Account section in the drawer

If we ever want per-user features (gr.OAuthProfile for logging the
generating user, gr.OAuthToken for HF API calls on their behalf),
re-enable both at that time.

README.md

@@ -8,8 +8,7 @@ sdk_version: "5.50.0"
 app_file: app.py
 python_version: "3.11"
 suggested_hardware: zero-a10g
-hf_oauth: true
-hf_oauth_expiration_minutes: 480
+hf_oauth: false
 preload_from_hub:
   - Comfy-Org/ltx-2 split_files/text_encoders/gemma_3_12B_it.safetensors
   - Kijai/LTX2.3_comfy diffusion_models/ltx-2.3-22b-dev_transformer_only_bf16.safetensors,loras/ltx-2.3-22b-distilled-lora-dynamic_fro09_avg_rank_105_bf16.safetensors,text_encoders/ltx-2.3_text_projection_bf16.safetensors,vae/LTX23_audio_vae_bf16.safetensors,vae/LTX23_video_vae_bf16.safetensors,vae/taeltx2_3.safetensors

app.py

@@ -466,13 +466,6 @@ def build_app() -> gr.Blocks:
             # Drawer (drawer behaves as fixed sidebar ≥1024 px;
             # absolute-positioned overlay <1024 px — see _CUSTOM_CSS).
             with gr.Column(scale=1, min_width=200, elem_classes=["aio-drawer"]):
-                if os.getenv("OAUTH_CLIENT_ID"):
-                    gr.Markdown("Account", elem_classes=["aio-drawer-heading"])
-                    gr.LoginButton(
-                        value="Sign in for Pro GPU quota",
-                        size="sm",
-                        elem_classes=["aio-login-btn"],
-                    )
                 gr.Markdown("Modes", elem_classes=["aio-drawer-heading"])
                 mode_buttons = {
                     name: gr.Button(